/*
 * Copyright 2003,2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.sf.cglib.core;

import net.sf.cglib.core.internal.Function;
import net.sf.cglib.core.internal.LoadingCache;
import org.objectweb.asm.ClassReader;

import java.lang.ref.WeakReference;
import java.security.ProtectionDomain;
import java.util.Map;
import java.util.Set;
import java.util.HashSet;
import java.util.WeakHashMap;

Abstract class for all code-generating CGLIB utilities.
In addition to caching generated classes for performance, it provides hooks for
customizing the ClassLoader, name of the generated class, and transformations
applied before generation.
/**
 * Abstract class for all code-generating CGLIB utilities.
 * In addition to caching generated classes for performance, it provides hooks for
 * customizing the <code>ClassLoader</code>, name of the generated class, and transformations
 * applied before generation.
 */
abstract public class AbstractClassGenerator<T>
implements ClassGenerator
{
    private static final ThreadLocal CURRENT = new ThreadLocal();

    private static volatile Map<ClassLoader, ClassLoaderData> CACHE = new WeakHashMap<ClassLoader, ClassLoaderData>();

    private static final boolean DEFAULT_USE_CACHE =
        Boolean.parseBoolean(System.getProperty("cglib.useCache", "true"));

    private GeneratorStrategy strategy = DefaultGeneratorStrategy.INSTANCE;
    private NamingPolicy namingPolicy = DefaultNamingPolicy.INSTANCE;
    private Source source;
    private ClassLoader classLoader;
    private String namePrefix;
    private Object key;
    private boolean useCache = DEFAULT_USE_CACHE;
    private String className;
    private boolean attemptLoad;

    protected static class ClassLoaderData {
        private final Set<String> reservedClassNames = new HashSet<String>();

        
AbstractClassGenerator here holds "cache key" (e.g. Enhancer configuration), and the value is the generated class plus some additional values (see unwrapCachedValue(Object). 
The generated classes can be reused as long as their classloader is reachable.
Note: the only way to access a class is to find it through generatedClasses cache, thus
the key should not expire as long as the class itself is alive (its classloader is alive).
/**
         * {@link AbstractClassGenerator} here holds "cache key" (e.g. {@link net.sf.cglib.proxy.Enhancer}
         * configuration), and the value is the generated class plus some additional values
         * (see {@link #unwrapCachedValue(Object)}.
         * <p>The generated classes can be reused as long as their classloader is reachable.</p>
         * <p>Note: the only way to access a class is to find it through generatedClasses cache, thus
         * the key should not expire as long as the class itself is alive (its classloader is alive).</p>
         */
        private final LoadingCache<AbstractClassGenerator, Object, Object> generatedClasses;

        
Note: ClassLoaderData object is stored as a value of WeakHashMap<ClassLoader, ...> thus this classLoader reference should be weak otherwise it would make classLoader strongly reachable and alive forever. Reference queue is not required since the cleanup is handled by WeakHashMap. /**
         * Note: ClassLoaderData object is stored as a value of {@code WeakHashMap<ClassLoader, ...>} thus
         * this classLoader reference should be weak otherwise it would make classLoader strongly reachable
         * and alive forever.
         * Reference queue is not required since the cleanup is handled by {@link WeakHashMap}.
         */
        private final WeakReference<ClassLoader> classLoader;

        private final Predicate uniqueNamePredicate = new Predicate() {
            public boolean evaluate(Object name) {
                return reservedClassNames.contains(name);
            }
        };

        private static final Function<AbstractClassGenerator, Object> GET_KEY = new Function<AbstractClassGenerator, Object>() {
            public Object apply(AbstractClassGenerator gen) {
                return gen.key;
            }
        };

        public ClassLoaderData(ClassLoader classLoader) {
            if (classLoader == null) {
                throw new IllegalArgumentException("classLoader == null is not yet supported");
            }
            this.classLoader = new WeakReference<ClassLoader>(classLoader);
            Function<AbstractClassGenerator, Object> load =
                    new Function<AbstractClassGenerator, Object>() {
                        public Object apply(AbstractClassGenerator gen) {
                            Class klass = gen.generate(ClassLoaderData.this);
                            return gen.wrapCachedClass(klass);
                        }
                    };
            generatedClasses = new LoadingCache<AbstractClassGenerator, Object, Object>(GET_KEY, load);
        }

        public ClassLoader getClassLoader() {
            return classLoader.get();
        }

        public void reserveName(String name) {
            reservedClassNames.add(name);
        }

        public Predicate getUniqueNamePredicate() {
            return uniqueNamePredicate;
        }

        public Object get(AbstractClassGenerator gen, boolean useCache) {
            if (!useCache) {
              return gen.generate(ClassLoaderData.this);
            } else {
              Object cachedValue = generatedClasses.get(gen);
              return gen.unwrapCachedValue(cachedValue);
            }
        }
    }

    protected T wrapCachedClass(Class klass) {
        return (T) new WeakReference(klass);
    }

    protected Object unwrapCachedValue(T cached) {
        return ((WeakReference) cached).get();
    }

    protected static class Source {
        String name;
        public Source(String name) {
            this.name = name;
        }
    }

    protected AbstractClassGenerator(Source source) {
        this.source = source;
    }

    protected void setNamePrefix(String namePrefix) {
        this.namePrefix = namePrefix;
    }

    final protected String getClassName() {
        return className;
    }

    private void setClassName(String className) {
        this.className = className;
    }

    private String generateClassName(Predicate nameTestPredicate) {
        return namingPolicy.getClassName(namePrefix, source.name, key, nameTestPredicate);
    }

    
Set the ClassLoader in which the class will be generated.
Concrete subclasses of AbstractClassGenerator (such as Enhancer)
will try to choose an appropriate default if this is unset.

Classes are cached per-ClassLoader using a WeakHashMap, to allow
the generated classes to be removed when the associated loader is garbage collected.
Params:
classLoader – the loader to generate the new class with, or null to use the default/**
     * Set the <code>ClassLoader</code> in which the class will be generated.
     * Concrete subclasses of <code>AbstractClassGenerator</code> (such as <code>Enhancer</code>)
     * will try to choose an appropriate default if this is unset.
     * <p>
     * Classes are cached per-<code>ClassLoader</code> using a <code>WeakHashMap</code>, to allow
     * the generated classes to be removed when the associated loader is garbage collected.
     * @param classLoader the loader to generate the new class with, or null to use the default
     */
    public void setClassLoader(ClassLoader classLoader) {
        this.classLoader = classLoader;
    }

    
Override the default naming policy.
Params:
namingPolicy – the custom policy, or null to use the default
See Also:
DefaultNamingPolicy/**
     * Override the default naming policy.
     * @see DefaultNamingPolicy
     * @param namingPolicy the custom policy, or null to use the default
     */
    public void setNamingPolicy(NamingPolicy namingPolicy) {
        if (namingPolicy == null)
            namingPolicy = DefaultNamingPolicy.INSTANCE;
        this.namingPolicy = namingPolicy;
    }

    
See Also:
setNamingPolicy/**
     * @see #setNamingPolicy
     */
    public NamingPolicy getNamingPolicy() {
        return namingPolicy;
    }

    
Whether use and update the static cache of generated classes
for a class with the same properties. Default is true.
/**
     * Whether use and update the static cache of generated classes
     * for a class with the same properties. Default is <code>true</code>.
     */
    public void setUseCache(boolean useCache) {
        this.useCache = useCache;
    }

    
See Also:
setUseCache/**
     * @see #setUseCache
     */
    public boolean getUseCache() {
        return useCache;
    }

    
If set, CGLIB will attempt to load classes from the specified
ClassLoader before generating them. Because generated
class names are not guaranteed to be unique, the default is false.
/**
     * If set, CGLIB will attempt to load classes from the specified
     * <code>ClassLoader</code> before generating them. Because generated
     * class names are not guaranteed to be unique, the default is <code>false</code>.
     */
    public void setAttemptLoad(boolean attemptLoad) {
        this.attemptLoad = attemptLoad;
    }

    public boolean getAttemptLoad() {
        return attemptLoad;
    }
    
    
Set the strategy to use to create the bytecode from this generator.
By default an instance of {@see DefaultGeneratorStrategy} is used.
/**
     * Set the strategy to use to create the bytecode from this generator.
     * By default an instance of {@see DefaultGeneratorStrategy} is used.
     */
    public void setStrategy(GeneratorStrategy strategy) {
        if (strategy == null)
            strategy = DefaultGeneratorStrategy.INSTANCE;
        this.strategy = strategy;
    }

    
See Also:
setStrategy/**
     * @see #setStrategy
     */
    public GeneratorStrategy getStrategy() {
        return strategy;
    }

    
Used internally by CGLIB. Returns the AbstractClassGenerator
that is being used to generate a class in the current thread.
/**
     * Used internally by CGLIB. Returns the <code>AbstractClassGenerator</code>
     * that is being used to generate a class in the current thread.
     */
    public static AbstractClassGenerator getCurrent() {
        return (AbstractClassGenerator)CURRENT.get();
    }

    public ClassLoader getClassLoader() {
        ClassLoader t = classLoader;
        if (t == null) {
            t = getDefaultClassLoader();
        }
        if (t == null) {
            t = getClass().getClassLoader();
        }
        if (t == null) {
            t = Thread.currentThread().getContextClassLoader();
        }
        if (t == null) {
            throw new IllegalStateException("Cannot determine classloader");
        }
        return t;
    }

    abstract protected ClassLoader getDefaultClassLoader();

    
Returns the protection domain to use when defining the class.

Default implementation returns null for using a default protection domain. Sub-classes may
override to use a more specific protection domain.

Returns:
the protection domain (null for using a default)/**
     * Returns the protection domain to use when defining the class.
     * <p>
     * Default implementation returns <code>null</code> for using a default protection domain. Sub-classes may
     * override to use a more specific protection domain.
     * </p>
     *
     * @return the protection domain (<code>null</code> for using a default)
     */
    protected ProtectionDomain getProtectionDomain() {
    	return null;
    }

    protected Object create(Object key) {
        try {
            ClassLoader loader = getClassLoader();
            Map<ClassLoader, ClassLoaderData> cache = CACHE;
            ClassLoaderData data = cache.get(loader);
            if (data == null) {
                synchronized (AbstractClassGenerator.class) {
                    cache = CACHE;
                    data = cache.get(loader);
                    if (data == null) {
                        Map<ClassLoader, ClassLoaderData> newCache = new WeakHashMap<ClassLoader, ClassLoaderData>(cache);
                        data = new ClassLoaderData(loader);
                        newCache.put(loader, data);
                        CACHE = newCache;
                    }
                }
            }
            this.key = key;
            Object obj = data.get(this, getUseCache());
            if (obj instanceof Class) {
                return firstInstance((Class) obj);
            }
            return nextInstance(obj);
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        }
    }

    protected Class generate(ClassLoaderData data) {
        Class gen;
        Object save = CURRENT.get();
        CURRENT.set(this);
        try {
            ClassLoader classLoader = data.getClassLoader();
            if (classLoader == null) {
                throw new IllegalStateException("ClassLoader is null while trying to define class " +
                        getClassName() + ". It seems that the loader has been expired from a weak reference somehow. " +
                        "Please file an issue at cglib's issue tracker.");
            }
            synchronized (classLoader) {
              String name = generateClassName(data.getUniqueNamePredicate());              
              data.reserveName(name);
              this.setClassName(name);
            }
            if (attemptLoad) {
                try {
                    gen = classLoader.loadClass(getClassName());
                    return gen;
                } catch (ClassNotFoundException e) {
                    // ignore
                }
            }
            byte[] b = strategy.generate(this);
            String className = ClassNameReader.getClassName(new ClassReader(b));
            ProtectionDomain protectionDomain = getProtectionDomain();
            synchronized (classLoader) { // just in case
                if (protectionDomain == null) {
                    gen = ReflectUtils.defineClass(className, b, classLoader);
                } else {
                    gen = ReflectUtils.defineClass(className, b, classLoader, protectionDomain);
                }
            }
            return gen;
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        } finally {
            CURRENT.set(save);
        }
    }

    abstract protected Object firstInstance(Class type) throws Exception;
    abstract protected Object nextInstance(Object instance) throws Exception;
}